This invention relates generally to apparatus for stabilizing, supporting, and elevating foundations for buildings, and in particular to the foundation slabs for buildings.
A problem with respect to the settling of the foundations of buildings is common in certain soil conditions, with resultant damage to building structures, including cracks and fissures in the walls, foundation, and foundation slabs. This problem has been addressed extensively in the prior art through the development and use of various types of foundation-shoring and lifting devices incorporating a bracket, normally of right angle configuration, so as to provide a lift arm which engages under the footing or vertical wall of a building foundation in such a way as to support the building wall. The lift arm provides an upward, reaction force to lift the foundation and wall in response to the operation of one or more hydraulic cylinders utilized in combination with the foundation bracket to drive pilings or pier pipe into the ground under the foundation. U.S. Pat. No. 4,925,345, having the same inventors as those named hereon, discloses such apparatus. Apparatus of the same general type particularly adapted to engage, support, and lift the perimeter foundation footing and vertical walls of building is also disclosed in U.S. Pat, Nos. 4,673,315, 4,695,203, and 3,796,055, as well as in other patents referenced in the aforesaid U.S. Pat. No. 4,925,345.
Insofar as is known, none of the apparatus disclosed in prior art patents and in use is particularly adapted for the supporting and lifting of horizontal foundation slabs of buildings. Such slabs frequently have an extensive lateral expanse, with their peripheral edge portions resting on or abutting the peripheral foundation footing of buildings. Such slabs also tend to settle and buckle, particularly in the middle between the supporting foundation walls and footings.
The attempted use of prior art lift apparatus of the aforesaid type to support and lift floor or foundation slabs has not been satisfactory for several reasons. In many instances, the foundation or floor slab of a building is not firmly in engagement with or supported by the outside footing or grade beam. Thus, when the prior art lift brackets are utilized to lift the outer, perimeter foundation or footing, the floor slab is not elevated with the outer footing. Also, floor slabs normally have a relatively small thickness on the order of four inches, and frequently have been weakened by settling. As a result, the floor slabs do not have good side-to-side and end-to-end strength permitting them to be lifted along with the perimeter footing or foundation, even when a plurality of lift brackets are utilized around the perimeter of a settled building. When perimeter lifting with prior art lift brackets is utilized in such a way, the slab frequently tends to settle in the center.
An alternative approach has been the attempted use of existing lift apparatus by cutting an opening in the foundation slab inside the building and inserting the lift bracket under the slab. However, the size and shape of existing lift brackets as disclosed in the above-referenced patents requires cutting an unduly large opening in basement or foundation slabs. Moreover, the right angle shape of such prior lift brackets as shown, for example, in U.S. Pat. No. 4,925,345, results in an uneven lifting force being applied under a foundation slab only on one side of the vertical line of force being delivered by hydraulic cylinders through a single, laterally extending, right angle lift arm.
Another known technique for stabilizing foundations, including slabs, involves pumping grout in the form of a slurry mixture of sand and/or gravel and cement under the foundation and slab. Such a foundation-stabilizing method is disclosed in U.S. Pat. Nos. 2,853,858 and 3,269,126 to Mintz and Freeman, Jr., respectively. The grout-pumping technique is expensive, and also not altogether satisfactory when the support and elevation of a slab over a large lateral span is required.
Having in mind the problems and disadvantages associated with the prior art efforts to support and lift foundation slabs having a relatively large lateral span, we have developed an improved slab support and lift apparatus which overcomes such problems.